About Regenerative Braking

Simply, regenerative braking enables the vehicle to capture some of the energy that would otherwise be lost when the vehicle slows to a stop. In conventional brake designs, the forward momentum of the vehicle is lost when the brakes are applied. This energy is converted to heat via friction and is dissipated into the surrounding air.

In hybrid cars with regenerative braking, some of the forward momentum of the car is captured and stored in batteries that provide power for accessories or locomotion. Regenerative brakes will slow the car and capture some of the "lost" energy, but they will not reliably bring the car to a complete halt.

Regenerative braking systems use the energy that would ordinarily be dissipated as heat to power a motor that is also wired to function as a generator. When the vehicle is in motion, the wheels turn the motor, generating current that aids the forward momentum of the vehicle. When the brakes are applied, the current flow in the motor reverses and causes the motor to oppose the vehicle's forward motion.

The applied braking force is proportional to the current that opposes forward motion. The current produces a force in the motor called torque, which slows the vehicle and allows the motor to charge the battery pack. The regenerative braking process slows the vehicle but not enough to bring the car to a precise stop.

For safety reasons, a regenerative braking system is typically used in parallel with a traditional friction brake design. Under most normal driving conditions, regenerative braking would be desirable in a hybrid electric vehicle. Under emergency braking conditions, however, the vehicle requires immediate maximum braking force, which can be delivered only by conventional friction brakes.

There are a few other reasons to use dual brake designs on hybrid vehicles. Most passenger vehicles are classified as two-wheel drive. Since regenerative braking systems are employed only on the vehicle's drive wheels, a set of friction brakes on the vehicle's unpowered wheels is also needed. Conventional brake systems, which are used on all of the vehicle's wheels, also act as an active back up in case the regenerative brakes fail under normal driving conditions.

Having two brake systems sounds like a good idea from a safety perspective, but it also means that the actions of these two independent systems need to be coordinated to balance energy recovery with the need for braking precision. Conventional designs accomplish braking via mechanical means. Brake systems are hydraulic, and use fluid power to generate and control the required braking forces. The brakes themselves are attached to the wheels. Most commonly, drum brakes or disc brakes are used along with highly heat-resistant material called brake pads or "shoes." The shoes, (or calipers in disc brakes) are mechanically forced against the drum (or discs) to slow the wheels to a stop. The force that presses the shoes or calipers against the wheel's brake system can also be generated hydraulically or pneumatically ("air brakes"). Electromagnetism can also be used to generate braking forces.

In hybrid electric vehicles, coordinating the actions of two braking systems requires extremely precise control. Mechanical components don't react fast enough to provide precise braking controls. A network of electronic controllers, sensors and actuators distributed throughout the vehicle is increasingly used in automotive braking designs. Electronic braking control is a major departure from the largely mechanical process of braking. Inclusion of these "brake-by-wire" technologies also enables other braking and safety technologies like collision detection and corrective braking.

Within an electromechanical braking system, a bevy of sensors track the wheel speed, the positions of the brake pedal and the emergency brakes, the actions of the throttle and steering systems, and the position and movement of the vehicle. Electromechanical braking employs other sensors to control how forcefully the brake should be applied and to measure the build-up of heat within the brakes.

The brake system must know all of this information at all times. In addition, the brake system must determine when to deploy safety mechanisms like anti-lock brakes, and must also track and work with other systems that are designed to improve the stability of the vehicle in sudden driving emergencies.

Regenerative brakes are neither new nor limited to automobiles. The technology was developed more than 40 years ago and is often found on other transports, like electric trains and large trucks where fuel economy is critical. Regenerative braking can save wear and tear on mechanical braking components and improve fuel economy in a vehicle by using more of the power train's output and providing a ready source of power to recharge batteries that would otherwise be depleted in the early stages of a trip.

Regenerative braking is not used on conventional vehicles. In a conventional vehicle, the battery is used to start the engine and to power the electrical accessories and control components. The alternator serves as a highly efficient recharger once the engine is started. The design of a conventional vehicle gives little reason to use regenerative braking.

Other "hybrid" technologies, like stop-start, can be used on conventional vehicles. Stop-start cuts the internal combustion engine when the car is idling and immediately restarts the motor when the gas pedal is pressed. Like regenerative braking, stop-start is not new, nor is it used exclusively on hybrids. It has come into vogue with hybrids as a way to improve fuel economy and conserve energy when the car is idling. Stop-start could reduce fuel consumption by 7-10% in a vehicle (hybrid or otherwise) outfitted with the technology.

Frazer-Nash Rises From The Ashes With A Tiger

The vehicle has a top speed of more than 187 mph, a fuel economy of better than 90 miles per gallon and will go from 0 to 60 in just 3.5 seconds. With a truly European flair, the vehicle features an 814 cc engine and four electric motors. The engine charges a lithium polymer cell in the vehicle and the hybrid system has a combined output of 370-hp.

The drive train was designed by Frazer-Nash, which is now a division of Kamkorp. The interior is designed with British luxury in mind. The vehicle was built in Turin at Italdesign's design and engineering center. The body is made from carbon fiber and weighs less than 250 pounds. Its design was inspired by the Frazer-Nash company's diamond-shaped logo.

Frazer-Nash hasn't built a vehicle in more than 50 years. The company spends most of its time these days designing hybrid drive trains for cars and mass transit systems. Despite the welcoming the car received in Geneva, don't expect Frazer-Nash dealerships to start popping up like McDonald's, The company has no plans to mass produce the vehicle.

Photo: Courtesy of Italdesign

Hydraulic Biodiesel Hybrid To Debut At Denver Auto Show

The three-door vehicle is powered by a 240-hp biodiesel hydraulic drive train and also features cameras in place of side view mirrors to increase efficiency and decrease drag. The LH4 has no conventional transmission, which makes the car lighter and more fuel-efficient. The company also says that the vehicle recaptures 100 percent of the energy lost when braking.

Lightning Hybrids is working on the development of a three-wheeled vehicle that uses the same drive train, and will create a retrofit kit that makes the drivetrain available to other vehicles. Once in production, the vehicle will sell for between $39,000 and $59,000. The cars and retrofit kits are expected to be available in mid-2010.

Photo Credit: Lightning Hybrids

CMU Says Volt Won't Be A Consumer Hit

Despite GM's protestations about the desirability of the car's 40-mile all-electric range, the cost to manufacture and replace the Li-ion battery pack will doom the car's commercial success, and relegate it to a collector curiosity. According to the report, smaller cars with smaller battery packs will provide better consumer value than the Volt will. Hybrids with an all-electric range of ten miles or less or improvements to current hybrid design will more likely provide the consumer with the right mix of fuel efficiency, acquisition and operational costs, and charging times.

Jeremy Michalek wrote a professor of engineering at CMU the study, which will be published in a future issue of Energy Policy. The research team constructed computer models of PHEVs that account for the impact of various battery sizes on fuel economy, greenhouse gas emissions and charging cycles.

The study found that for moderate travel, which the group defined as those trips between 20 and 100 miles, PHEVs produced fewer greenhouse gas emissions, but fell short on cost-effectiveness. The models indicated that hybrid electric vehicles were more cost efficient with the study's controls. PHEVs became more attractive from a cost perspective only when the price of fuel was high, the price of batteries was low, the cost of electricity generation was reduced or other costs, like carbon taxes, were added to the model.

Carbon taxes are not currently applied as such, however the automakers do face fines if the combined average fuel economy of their fleet does not meet federal standards. Regulations do not govern the tailpipe emissions of any model in particular, so models with lower fuel efficiency and higher carbon emissions can be offset by sales of higher fuel economy models from the same manufacturer.

Recently, several states won the right to regulate tailpipe emissions, a reversal of a long-standing policy that preserved federal control of vehicle emissions. The change in policy means that states can enact tougher emissions standards than those imposed by the federal government. Even with increased restrictions on emissions, and changes to other study variables, the author concludes that the most effective PHEVs will be small urban vehicles whose drivers have access to regular charging facilities.

Source: Carnegie Mellon University PDF link

Photo Credit: MR38

FEV Opens Hybrid, EV Development Center

The HEVDC will facilitate the development of hybrid power trains and related technologies by providing accurate testing facilities. The facility will initially test hybrid power trains and transmissions, electric motors, and charging stations for EVs and PHEVs. The HEVDC's charging station is the first in Michigan and will also be used for testing and validation purposes.

The HEVDC features multiple battery emulation systems and a chassis dynamometer to facilitate testing while minimizing downtime. The setup also permits full testing of all hybrid system components at once. The HEVDC can test powertrains of any size and the battery emulators can provide as much as 900V on demand, about three times that required of today's HEVs.

The testing center will help automotive manufacturers test hybrid powertrain designs, as well as integration of those designs into pre-production and production vehicles.

FEV says that it expects to add personnel to meet the demand for the testing center. FEV provides gasoline, diesel and electric powertrain engineering, design and testing services for a variety of commercial automotive applications.

Photo Credit: FEV

Wow!

Despite the glum predictions, Toyota says it still expects to sell about 67,000 hybrid vehicles, a 15 percent increase over 2008 sales figures. The company also says it believes it can meet its 2010 sales goal of 400,000 units of the new Prius in 2010. Toyota also uncovered the RX450h Lexus hybrid, which it plans to sell in Europe in 2010.

Slow sales haven't stopped the competition, however. Nissan introduced a diesel-electric concept that sports a look reminiscent of the Fisker Karma or Tesla Roadster. The Essence two-seat luxury hybrid sedan features a 434hp, 3.7L diesel engine coupled with a 158hp electric motor. The company hasn't said whether it plans to put the vehicle in production, but did announce plans to study the construction of a lithium-ion battery plant in Portugal, leaving many to speculate that a production version of the Essence will see the light of day.

Last year, the national government in Portugal announced plans to build a nationwide charging network for plug-in electric vehicle as part of its plans to reduce CO2 emissions. Renault-Nissan will begin selling electric vehicles in Portugal in 2011, and also has zero-emission plans in Denmark, Monaco, Yokahama, Japan, Tennessee, Oregon and California.

New Hybrid Technology May Cut Fuel Consumption In Half

Artemis Intelligent Power has converted a BMW 530 sedan to demonstrate the system. The computer-controlled hydraulic transmission system outperforms other hydraulic hybrid designs. Under test conditions in Europe, the modified BMW 530 used 52.7 percent less fuel than a regular gasoline-powered BMW530i. The system was also tested in the US under more aggressive test circumstances. In addition to a significant reduction in gasoline consumption, the modified prototype reduces carbon emissions by 30 percent.

In the US, the system achieved a reduction in fuel consumption of one-third, which compares favorably to the Toyota Prius and other highly fuel-efficent hybrids. The engineers at Artemis Intelligent Power are confident that the technology will be widely adopted in the next decade because it is cheaper to produce than current hybrid electric drive trains, and could eliminate the "hybrid premium" that currently prevents more drivers from adopting the technology. The company has already licensed the technology to commercial partners, including Bosch-Rexroth.

Photo Credit: Artemis Intelligent Power

Toyota Puts Hybrid Development Into High Gear

Most electrical power plants in the United States are fired by coal, natural gas or petroleum, all of which release carbon dioxide into the air. Coal, the most common power plant fuel, releases the most CO2 into the atmosphere as it is burned to make electricity. Natural gas, less commonly used in power plants, is cleaner by a scant 50 percent.

In a head-to-head comparison, an all-electric vehicle such as a Tesla Roadster that charges off of house current might actually be responsible for more CO2 emissions than a Prius or Insight would when the emissions from a coal-fired power plant are taken into consideration. Hybrid cars also emit less CO2 than most highly efficient gasoline-only vehicles and those powered by diesel or "clean diesel" engines.

So do EVs and PHEVs make sense? If you're switching to one from a larger, older or less efficient vehicle, a PHEV or EV can indeed reduce your carbon footprint. The story raises an issue, however, that has been discussed before. The overall impact of large-scale migration to PHEVs, EVs and HEVs won't reduce carbon emissions significantly unless the fossil-fueled power plants are modernized at the same time. Conversion of the plants to natural gas can reduce carbon emission, but the cost of a natural gas-fired plant will substantially increase consumer cost and will reduce the rate at which consumers convert to vehicles with electric drive trains.

One potential alternative is a hydrogen-powered vehicle. BMW has tested its hydrogen FCV at Argonne National Laboratories, and those tests show that the vehicle actually emits air that is slightly cleaner than the air it takes in. Unfortunately, the vehicle won't be mass-produced anytime in the near future because the supporting infrastructure is not yet available.

The moral of the story? If you're buying an alternative-fuel vehicle for environmental reasons, make sure that you're really helping Mother Nature, and not just shifting the problem to someone else's exhaust pipe.

Source: International Business Times

Photo: Courtesy of Toyota